Activated carbon has the property of adsorbing hydrocarbon rich gas, including methane or natural gas and allowing one to store more of the gas in a tank of a given volume than the tank would hold in the absence of carbon. However, there are problems involved in the handling of carbon preventing successful commercial utilization of the process. For example, carbon in the form of a fine powder or particles which may catch fire when exposed to air and possible dust explosions present a serious hazard. Also carbon in the form of a fine powder or particles presents serious respiratory toxic risks upon inhalation. Additionally, these forms of carbon have a tendency to be embedded and travel with the gas when it is released. Carbon particles are known to clog valves and equipment and are detrimental to equipment with moving parts. In the past there is art wherein the carbons are formed into structured systems which are placed into storage tanks. This potential solution increases the cost of the carbon and the cost of the tank into which it is placed.
Various methods have been utilized to store and/or to increase the storage capacity of tanks utilized for the storage of natural gas. U.S. Pat. No. 5,548,258 discloses the use of hydroxy phenoxyether polymer barrier liner for use in a tank storing compressed natural gas (CNG). U.S. Pat. No. 5,603,360 describes the use of a flexible bladder for the transportation of gas from a pipeline to a CNG automobile re-fueling station. U.S. Pat. No. 5,676,180 further describes the use of this bladder as a storage means for CNG at the automobile re-fueling station or other end user locations. U.S. Pat. No. 6,217,626 discloses the use of selected additives which allows one to store the natural gas at pressures around 1000 psia. For storage or pipeline transportation of natural gas at pressures over 800 psia it was found advantageous to add ammonia to the natural gas. U.S. Pat. No. 6,613,126 discloses a method of separating natural gas into a high carbon component and a low carbon component and using two tanks with adsorbent that will adsorb either the high carbon or the low carbon fraction. They used activated carbon for the absorption of natural gas which required that normal paraffin be pre-absorbed on the activated carbon prior to the absorption of natural gas. This method requires the re-mixing of the components upon releasing from the storage tanks and prior to use. The natural gas can not go into the end use apparatus without this mixing step prior to utilization.
U.S. Pat. No. 4,999,330 discloses a process wherein bulk carbon is reduced in bulk from about 50% to 200% which gives an increase in absorption capacity of about 50 to 200% in density. This process was found useful in low pressure storage of CNG. This process also calls for the use of a binder such as methyl cellulose.
Some activated carbons can increase the capacity of gas storage in a tank. The gas molecules are held on the surface of the carbon (science of surface chemistry) and thus the amount of gas that can be stored in a tank increases based on the available carbon surface area. The economics connected with such carbons makes them unattractive being sold at prices ranging from US$50 to US$125 per pound. These materials do not solve the problem at a financial cost that would allow the materials to be used in increased mass storage of natural gas. Additionally these materials do not allow for convenient filling and use of the methane or natural gas.
There was given in literature sources a carbon that appeared to have the necessary gas adsorption characteristics; i.e., the carbon could store twice or more the amount of natural gas in the same volume at the same pressure, e.g. ambient temperatures at 3,000 psia, in the same size tank. The carbon was identified as AX-21 and upon testing it was found capable of storing 2.6 times the amount of methane in the same tank as that tank without the presence of AX-21. This carbon is no longer manufactured and if available the price was given as $50 a pound by the manufacturer for purchases in large volume. The characteristics of this particular carbon are given in Table 1.
Table 1 lists the samples and the “surface area” of the carbon sample as measured by the adsorption of nitrogen in a specific test. The results for surface area are available for many adsorbents from commercial suppliers. However, nitrogen is not methane and, as the Table shows, it was found that the correlation between the nitrogen capacity and the methane capacity is very weak. Suitable carbons cannot be found simply by selecting low density, high surface area carbons.
A carbon surface contaminated by undesirable adsorbates has limited capacity for additional binding. Freshly prepared activated carbon typically has a clean surface. Activated carbon production with heating drives off potential adsorbates including water leading to a surface with high adsorptive capacity. While activated carbon has been used in some applications to remove selected hydrocarbons from water these applications teach away from the use in this particular application as water would interfere with the ability of the carbon to adsorb sufficient gas to enable one to store about twice the quantity of gas within a storage container. It is known that humidity is one of the factors that influence the adsorptive properties of active carbon in air.
Accordingly, a method, device and/or system of a carbon material stored, charged and discharged with gas having reduced risks of fire, explosion and ability to stored at least twice the volume of gas as normally stored is needed.